Ignition circuit for a discharge lamp



June 15, 1965 HOWELL 3,189,789

IGNITION CIRCUIT FOR A DISCHARGE LAMP Filed July 2, 1962 Invervtov Edw dHeh HoweLL b8 9%! is tovneg electron emission. lamp, the arc drops wellbelow the range of the power United States Patent M 3,189,789 IGNITIONCIRCUIT FOR A DISCHARGE LAMP Edward Keith Howell, Hendersonville, N.C.,assignor to General Electric Company, a corporation of New York FiledJuly 2, 1%2, Ser. No. 266,597 5 Claims. (Cl. 315-441) This inventionrelates in general to circuits for discharge lamps and, moreparticularly, to a high voltage pulse generating circuit for thestarting of a high intensity discharge lamp.

The high intensity discharge lamp to be started is a Xenon arc dischargelamp. This lamp is rated to operate at 100 amperes, 20 volt DC. and thusis well within the range of a battery energy output. The lamp is a twoelectrode polarized arc lamp with a thoriated tungsten cathode andtungsten anode. Initially a high voltage pulse of 30-50 kv. must beapplied across the terminal to form a conduction path within the lamp.This must be immedi ately followed by a high current discharge from asource of at least 65 volt DC to form a cathode hot spot for Uponemission and starting of the supply and the normal operation follows at100 amps, 20 volt. An example of the above lamp is disclosed in US.Patent 2,965,790Ittig et al., issued December 20, 1960.

It is an object of this invention to provide an improved pulsegenerating circuit for the above lamp and similar discharge lamps whichdevelops a series of high voltage pulses for initiating conduction inthe lamp from a source of pulsating current.

It is a further object of this invention to provide such a pulsegenerating circuit which utilizes an electron control device having apredetermined voltage breakdown invention provides a pulse generatingcircuit for a discharge lamp requiring a very high voltage forinitiating conduction therein which comprises a controlled rectifierconnected to a source of pulsating current and having a controlledelectrode, means for rendering the controlled rectifier conductiveincluding a zener diode conected to the gate of the controlledrectifier, and means for delivering a high voltage pulse to the lampwhen the'gate of the silicon controlled rectifier is rendered conductiveincluding an operating capacitor connected to the controlled rectifierand the lamp.

Further objects and advantages of the invention will appear from thefollowing specification.

A preferred embodiment of the invention is shown in the drawing.

In the drawing, an operating circuit for discharge lamp 11 includes alow Voltage direct current source, such as a battery 12, conductor 13, acontrol switch 14, conductor 15, a current-limiting impedance 16,conductor 17, high current rectifier 18, conductor 19, autotransformercoil 20, conductor 21 and conductor 22 to ground.

Patented June 15, 1965 The discharge lamp 11, as shown, is a xenon arcdischarge lamp comprising an envelope 23 filled with xenon gas andprovided with a thoriated tungsten anode 24 and tungsten cathode 25. Thelamp operates 100 amps at 20 volt D.C.; hence, the source 12 can be a27.5 volt storage battery as is customarily provided on certainvehicles. However, to ignite the lamp, a 3050,000 volt pulse must beapplied across the lamp electrode to initially ionize the gas. 7

For starting the lamp there is provided a step-up inverter rectifier 26,having a pulsating intermediate voltage output, connected betweenconductors 15 and 22 by conductors 27 and 28. The output from theinverter rectifier 26 is directed to storage capacitor 29 through aresistor 30, resistor 31, conductor 32, and which storage capacitor bankis connected to ground by conductor 33 so that the capacitor is chargedat the intermediate volt age. The starting circuit further includespulse generating circuit, shown Within the dotted lines, 34, the outputof which is applied to anode 24 of the lamp 11 through autotransformercoil 20. The inverter rec-tifier circuit 26 may be of the type describedin co-pending application of Joe A. Nuckolls, Serial No. 206,613, filedJuly 2, 1962, and assigned to the same assignee.

The pulse generating circuit 34 is provided with a silicon controlledrectifier 38 connected to input conductor 35 through a resistance 39 byconductor 40. An operating capacitor 41 is connected to resistance 39 byconductor 42 and to ground by conductor 43 to form a charging circuitacross storage capacitor 29. The operating capacitor 41 provides thetriggering action for the control gate 44 of the controlled rectifier 38through zener diode 45 and diode 46. The zener diode 45, being asubstantially constant voltage electron control device, becomesconductive when the charge on the capacitor 41 reaches a predeterminedZener voltage level. When said level is reached, the diode &5 becomeconductive, triggering the silicon controlled rectifier 38 which drawsenergy from the capacitor 41 and discharges a high current pulse throughconductor 47, through primary 48 of a ringing transformer 49 andconductor 5% connecting the coil to ground. The series connection ofoperating capacitor 41, silicon controlled rectifier 38 and the primary48 thereby forms a discharge loop.

The secondary 51 of ringing transformer 49 is applied to a pulsetransformer circuit including the transformer 29, capacitor 52 and sparkgap 53 thereby forming an oscillatory circuit with primary 54 oftransformer 26 which induces a damped oscillatory train of high voltagepulses in the pulse transformer circuit. The high voltage I pulse fromtransformer 49 charges the capacitor 52 to warm up. When the voltagedrop across the lamp falls below a predetermined level, the inverterrectifier 26 is turned off through conductor 55 as described in theabovementioned co-pending application. Capacitors 56, 57 and 37 provideradio frequency bypassing.

:9 By way of specific example, the various components above referred tomay be the following:

The output of inverter rectifier 26 is approximately 170 volts at 300cycles per second. As the output of the inverter rectifier 26 is appliedto storage capacitor 29, and also to operating capacitor 41 of the pulsegenerating circuit, energy is stored therein. The zener diode 45 is asubstantially constant voltage device which conducts when the voltagerises to 100 volts (this voltage may be varied to suit the lamp startingrequirements); thus, at 100 volts, approximately joules of energy arestored in capacitor bank 29 and 0.5 joule in operating capacitor 41. At100 volts, the zener current applied to gate 44 of silicon controlledrectifier 38 is sufficient to make silicon controlled rectifier 38conductive, extracting approximately 0.5 joule from operating capacitor41 and delivering it through transformer 49. When the voltage dropsbelow 100 volts,

the zener diode becomes non-conductive and silicon con-.

trolled rectifier 38 is turned olf by the tendency of the inductance ofringing transformer 49 and capacitor 41 to oscillate and reverse thecurrent flow through silicon controlled rectifier 38. Capacitors 56 and57 serve also to limit the rate or rise of the voltage reapplied'to thecontrolled rectifier 38 to assure turn off of that device.

The 100 volt pulse is stepped up by the turns ratio 1:200 of transformer49 and the voltage on the capacitor 52 rises toward 20,000 volts. Thespark gap 53 breaks down when the voltage reaches 10,000 volts and thepulse is delivered into eliective primary 54 of the autotransformer 20.The step-up ratio of the autotransformer being 1:5, a kv., highfrequency pulse is provided to the lamp. The negative coefiicient ofresistance of the lamp after starting causes the arc drop across thelamp to fall below 100 volts after ignition, thus stopping the operationof the pulse generating circuit, since zener diode 45 does not triggerthe gate of silicon controlled rectifier 38. The 10 joules of energystored in the storage capacitor 29 serves to maintain operation of thelamp and develop a hot spot on the cathode, until the voltagedrop acrossthe lamp falls below the source voltage. At this point the sourcevoltage takes over operation of the lamp through current limitingresistor ballast 16 and high current rectifier 18. The efiect ofconductor 55 is such that when the current drawn by the lamp l1 rises toapproximately amperes the operation of the inverter rectifier 2s ceasesand no further charging of the storage capacitor 29 takes place duringoperation of the lamp.

While the invention has been specifically disclosed and the preferredembodiment thereof shown, it should be understood that the invention maybe widely modified within the spirit and scope of the appended claims.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A pulse generating circuit for a dischargelamp requiring a highvoltage pulse for initiating conduction ductive including an operatingcapacitor and a ringing therein comprising, a discharge lamp, acontrolled rectifier connected to a pulsating current source and havinga control electrode, means for rendering said controlled rectifierconductive including a zener diode connected to the source and to thecontrol electrode and means including an operating capacitor responsiveto the controlled rectifier when it is rendered conductive fordelivering a high voltage pulse to the lamp.

2. A pulse generating circuit for a discharge lamp requiring a highvoltage pulse for initiating conduction therein comprising, a dischargelamp, a silicon controlled rectifier connected to a pulsating currentsource and having a control electrode, means for rendering saidcontrolled rectifier conductive including an electron control devicewhich becomes conductive upon the application of a predetermined voltagelevel connected to the source and to the control electrode of thesilicon controlled rectifier and means including an operating capacitorand a stepup transformer responsive to the controlled rectifier when itis rendered conductive for delivering a high voltage pulse to the lamp.

3. A pulse generating circuit for a discharge lamp requiring a highvoltage pulse for initiating conduction therein comprising, a dischargelamp, a silicon controlled rectifier connected to a pulsating currentsource and having a control electrode, means for rendering saidcontrolled rectifier conductive including an electron control devicewhich becomes conductive upon the application of a predeterminedvoltage. level connected to. the source and to the control electrode ofthe silicon controlled rectifier and means for delivering a high voltagepulse to the lamp when the controlled rectifier is rendered conductiveincluding an operating capacitor, a step-up transformer connected to theoutput of said silicon controlled rectifier, a spark gap and asecondcapacitor connected to said transformer, said second capacitor beingcharged from the operating capacitor prior to the breakdown of saidspark gap.

4. A pulse generating circuit for a discharge lamp comprising, adischarge lamp, a controlled rectifier connected to a pulsating currentsource and having a control electrode, means for rendering saidcontrolled rectifier conductive including a zener diode connected to thesource and to the electrode of the controlled rectifier, an oscillatingcircuit for rendering said controlledrcctifier non-controde, means forrendering said controlled rectifier conductive connected to the sourceand to the control electrode of the controlled rectifier and meansincluding a charging capacitor and a spark gap connected to thecontrolled rectifier and lamp and responsive to the controlledrectifier-when conductive for delivering a high voltage pulse to thelamp, said capacitor being charged to a predetermined voltage levelprior to the breakdown of said spark gap.

Eieierences Cited by the Examiner UNITED STATES PATENTS 2,946,924 7/60Gerlach et al 31s 241 2,975,331 3/61 Diaz etal 3152859X 3,049,642 8/62Quinn 31s 206 DAVID J GALVIN, Primary Examiner.

JAMES D. KALLAM, Examiner.

1. A PULSE GENERATING CIRCUIT FOR A DISCHARGE LAMP REQUIRING A HIGHVOLTAGE PULSE FOR INITIATING CONDUCTION THEREIN COMPRISING, A DISCHARGELAMP, A CONTROLLED RECTIFIER CONNECTED TO A PULSATING CURRENT SOURCE ANDHAVING A CONTROL ELECTRODE, MEANS FOR RENDERING SAID CONTROLLEDRECTIFIER CONDUCTIVE INCLUDING A ZENER DIODE CONNECTED TO THE SOURCE ANDTO THE CONTROL ELECTRODE AND MEANS INCLUDING AN OPERACTING CAPACITORRESPONSIVE TO THE CONTROLLED RECTIFIER WHEN IT IS RENDERED CONDUCTIVEFOR DELIVERING A HIGH VOLTAGE PULSE TO THE LAMP.